In the field of microscopes used for scanning biological samples and the like, there is often the problem of obtaining a suitable amount of light from the target or sample in order to build a comprehensive image of an area of interest. This is especially the case when capturing image information corresponding to fluorescing samples, wherein, due to the fluorescence, the amount of light reaching a conventional detector array is not enough to provide a clear image of the target. In the art, this problem is typically solved using a time delay integration (TDI) sensor. This sensor is adapted to integrate a plurality of captured images of the target to produce a high quality image.
A prior art image scanning device for use in capturing image information from fluorescent samples is shown in FIG. 1. This conventional image scanning apparatus 1 comprises a lens assembly 20, a lens 10 and a time delay integration (TDI) sensor 80 for use in capturing image information. Typically, certain molecules within a sample 30 are labeled with a fluorescent marker or “fluorophore” that enables items of interest to fluoresce; for example, cancer cells within a tissue sample may be selectively labeled with the fluorescent marker. To subsequently activate these fluorophore molecules and enable fluorescence, the sample 30 must be irradiated with light of a first wavelength. This light is commonly referred to as the excitation radiation 15 and will comprise light within a set spectral band, typically ultra-violet radiation. This radiation 15 may be produced using an exciter source 40 which emits white light 5 comprising wideband spectral electro-magnetic (EM) radiation. Excitation filter 50 then filters this light so that only the spectral band making up the desired excitation radiation 15 is allowed to illuminate the sample 30. A dichroic beam splitter 60 is configured to reflect the excitation radiation 15 towards lens assembly 20, wherein the radiation 15 passes through the lens 10 before impinging upon the sample 30.
After impinging on the sample 30, the excitation radiation 15 excites the fluorescent molecules within the sample. These molecules then emit light 25 of a second wavelength or second spectral band, i.e. the fluorophore molecules fluoresce. Typically, this emitted light is within the visible spectrum. The light 25 emitted by the sample 30 then passes back through the lens assembly 20, wherein it is focused by the lens 10. After focusing, the emitted light 25 then continues to the dichroic beam splitter 60, which is configured to allow light of a second wavelength or within a second spectral band to pass through the beam splitter. After passing through the beam splitter 60 the emitted light 25 may be further filtered by emission filter 70. The emitted light 25 then impinges on the TDI sensor 80 and image information is captured.
One problem that exists with the apparatus shown in FIG. 1 is that the use of a TDI sensor 80 places limits upon the use of the microscope. As the TDI sensor typically integrates images of a particular area of the target, the system is sensitive to changes during the acquisition of each image used in the integration. This can then make activities such as focusing difficult to perform, as changes in focus cannot be made whilst capturing a particular image within the integrated set, as this would degrade the resultant integrated image.
In particular, when scanning biological samples and the like, it is often necessary to re-focus the objective lens rapidly in order to compensate for variations in thickness of a biological sample being inspected. The design of the TDI sensor makes it difficult to use the image information captured by the sensor to perform these focusing operations. Hence, there is a requirement for an image scanning apparatus using a TDI sensor that is able to rapidly refocus the objective lens in order to account for variations in biological samples.